Triple the speed of E2E tests and stop them exploding if a circular datastructure is logged (#8095)

* stop e2e tests exploding if a circular datastructure is logged

it's valid for the webapp to log datastructures to the console which happen to be circular
but the e2e test running explodes badly with a runtime exception and bombs out before
logging anything or providing a sensible stacktrace. you can trap the exception though and
get a sensible error however.

* don't barf on circular refs in return vals either

and log timestamps

* log timestamps

* speed up roomDir & E2EE tests by 3x

use timeouts correctly, so the first set
of scenarios take 42s to run rather than 2m21s

* speed up space test by 20s

test/end-to-end-tests/README.md

@@ -32,6 +32,12 @@ start.js accepts these parameters (and more, see `node start.js --help`) that ca
  - `--windowed` run the tests in an actual browser window Try to limit interacting with the windows while the tests are running. Hovering over the window tends to fail the tests, dragging the title bar should be fine though.
  - `--dev-tools` open the devtools in the browser window, only applies if `--windowed` is set as well.
 
+For god level debug (e.g. for debugging slow tests):
+
+`env DEBUG="puppeteer:*" ./test/end-to-end-tests/run.sh --app-url http://localhost:8080 --log-directory `pwd`/logs --dev-tools --windowed` 2>&1 | cat
+
+(piping everything through cat means you get proper timestamps on the debugging, and the chromiums hang around at the end)
+
 Developer Guide
 ===============
 
@@ -40,3 +46,4 @@ https://github.com/matrix-org/synapse/tree/master/CONTRIBUTING.rst
 
 Please follow the Matrix JS/React code style as per:
 https://github.com/matrix-org/matrix-react-sdk/blob/master/code_style.md
+